The usual model of this behavior in the framework of the heat diffusion equation is as a boundary condition of the third kind to in which the outward thermal flux is set equal to a heat transfer coefficient h times the difference between the surface and free-stream temperatures. For buoyancy-driven flows, a widely used method to treat this mechanism is to neglect density variation except where multiplied by the acceleration due to gravity – that method is the (*) Boussinesq approximation. Using the pi theorem on the aforementioned boundary condition, which is Newton's law of cooling, yields the Nusselt number, which scales with the relative strength of this mechanism. For 10 points, name this heat transfer mechanism by which thermal energy is carried away with fluid flow, as distinct from 
The usual model of this behavior in the framework of the heat diffusion equation is as a boundary condition of the third kind to in which the outward thermal flux is set equal to a heat transfer coefficient h times the difference between the surface and free-stream temperatures. For buoyancy-driven flows, a widely used method to treat this mechanism is to neglect density variation except where multiplied by the acceleration due to gravity – that method is the (*) Boussinesq approximation. Using the pi theorem on the aforementioned boundary condition, which is Newton's law of cooling, yields the Nusselt number, which scales with the relative strength of this mechanism. For 10 points, name this heat transfer mechanism by which thermal energy is carried away with fluid flow, as distinct from radiation and conduction.
The usual model of this behavior in the framework of the heat diffusion equation is as a boundary condition of the third kind to in which the outward thermal flux is set equal to a heat transfer coefficient h times the difference between the surface and free-stream temperatures.
{convection} [accept either {free convection} or {forced convection} as all {clues} apply {equally} to either]